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Date: Thu, 18 Jul 2013 05:49:50 +0300
From: Eli Zaretskii <eliz AT gnu DOT org>
Subject: Re: Set _IOERR if the file stream has been opened in wrong mode.
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> Date: Wed, 17 Jul 2013 22:47:28 +0200
> From: Juan Manuel Guerrero <juan DOT guerrero AT gmx DOT de>
> 
> According to http://pubs.opengroup.org/onlinepubs/009695399/functions/fgets.html
> RETURN VALUE
> 
>      Upon successful completion, fgets() shall return s. If the stream is at end-of-file,
>      the end-of-file indicator for the stream shall be set and fgets() shall return a null
>      pointer. If a read error occurs, the error indicator for the stream shall be set,
>      fgets() shall return a null pointer.
> 
> 
> According to http://pubs.opengroup.org/onlinepubs/009695399/functions/fputs.html
> RETURN VALUE
> 
>      Upon successful completion, fputs() shall return a non-negative number. Otherwise,
>      it shall return EOF, set an error indicator for the stream.
> 
> 
> According to http://pubs.opengroup.org/onlinepubs/009695399/functions/fread.html
> RETURN VALUE
> 
>      Upon successful completion, fread() shall return the number of elements successfully
>      read which is less than nitems only if a read error or end-of-file is encountered.
>      If size or nitems is 0, fread() shall return 0 and the contents of the array and the
>      state of the stream remain unchanged. Otherwise, if a read error occurs, the error
>      indicator for the stream shall be set
> 
> 
> According to http://pubs.opengroup.org/onlinepubs/009695399/functions/fwrite.html
> RETURN VALUE
> 
>      The fwrite() function shall return the number of elements successfully written,
>      which may be less than nitems if a write error is encountered. If size or nitems
>      is 0, fwrite() shall return 0 and the state of the stream remains unchanged.
>      Otherwise, if a write error occurs, the error indicator for the stream shall be set,
> 
> 
> For IEEE Std 1003.1-2001-conforming systems all the functions also shall set errno.

Thanks, but I've already read all that, and found nothing about
reading from a stream open as "w".  Who said that is an error?

> It is a matter of fact that the sample code posted in the previous mail
> behaves as described by me for linux and cygwin.  And this behavior is
> exploited by other programs like lua.  I have inspected __getc, __putc,
> fwrite and fread and neither of them set EOF.

filbuf.c sets EOF when __getc returns -1.

> BTW as can be seen for fgets if the stream is at end-of-file, the end-of-file
> indicator for the stream shall be set apart from returning a NULL pointer.

It already does that, AFAICS.